Node b and rnc actions during a serving hsdpa cell change

ABSTRACT

An apparatus and method in accordance with the present invention reduce the amount of data that is stalled in a source Node B after a serving HS-DSCH cell change in a communication system that includes a serving RNC and at least one Node B. In a first embodiment, the RNC temporarily suspends data transmissions from the RNC to the Node B. In a second embodiment, the activation time is used in data scheduling. In a third embodiment, a more robust MCS level is selected. In a fourth embodiment flow control is employed for the data transmitted between the RNC and the Node B.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.10/407,559, filed Apr. 4, 2003, which claims the benefit of U.S.Provisional Application Ser. No. 60/370,719, filed Apr. 5, 2002, whichare incorporated by reference as if fully set forth.

FIELD OF THE INVENTION

The present invention relates to the field of wireless communications.More specifically, the present invention relates to intelligentscheduling of data transmissions to reduce, and potentially avoid, datarecovery by high layers following handover.

BACKGROUND OF THE INVENTION

In the High Speed Downlink Packet Access (HSDPA) of a third generation(3G) cellular system for Frequency Division Duplex (FDD) and TimeDivision Duplex (TDD) modes, data in the form of Protocol Data Units(PDUs) for the High Speed Downlink Shared Channel (HS-DSCH) isdistributed (i.e., buffered and scheduled) in the Node B. Therefore, theRadio Network Controller (RNC) does not have an up-to-date status of thetransmissions of Protocol Data Units (PDU).

There are scenarios in which a User Equipment (UE) has to perform aserving HS-DSCH cell change to achieve improved radio conditions andavoid loss of the radio link. The serving HS-DSCH cell change is whenthe UE has to change the cell associated with the UTRAN access pointperforming transmission and reception of the serving HS-DSCH radio link.

The Node B associated with the cell before the serving HS-DSCH cellchange is called the source Node B and the Node B associated with thecell after the serving HS-DSCH cell change is called the target Node B.With HSDPA, since data is typically distributed in a Node B prior totransmission to the UE, when the UE performs a serving HS-DSCH cellchange it is possible that the UE stops transmission and reception inthe source cell before all of the PDUs currently stored in the sourceNode B are transmitted. Accordingly, there is a possibility thatconsiderable amounts of data buffered in the source Node B will be lost.The reason is at the moment of handover there is no mechanism within theUTRAN architecture that allows for transfer of the buffered data to thetarget Node B. When data is lost in the source Node B it can berecovered by the RNC, but at the cost of significant additionaltransmission latency that may result in inability to achieve the user'squality of service requirement.

A prior art method for processing data during a serving HS-DSCH cellchange is shown in FIG. 1. After the RNC recognizes the need for aserving HS-DSCH cell change, it sends a reconfiguration message to theNode B. This reconfiguration message may or may not specify anactivation time, which is an explicit moment in time that is known inthe Node B when the UE will stop listening to the HS-DSCH in that celland start receiving the HS-DSCH in a new cell. If there is no activationtime specified in the reconfiguration message, the UE will stoplistening to the HS-DSCH in the source cell and wait for receiving theHS-DSCH in a new cell until the Layer 1 connection to the new cell isestablished. Any data that is buffered in the Node B after theactivation time will be stalled in the Node B and is useless andtherefore will be discarded.

Upon receipt of the reconfiguration message, the Node B continues toschedule data to UEs based upon the priority of the data and latencyrequirements. The Node B then applies the appropriate modulation andcoding set (MCS), which is chosen by the scheduler, to the data fortransmission to the UEs. In current 3G systems, the MCS level is basedupon UE feedback that identifies the downlink channel quality to theNode B. Upon reception of the channel quality estimate, the Node Bdetermines the MCS primarily based on a mapping table predefined andknown by both the UE and the Node B. The mechanism to choose the MCSmay, for example, be based on reaching certain channel qualitythresholds. MCS choices range from less robust combinations that providea high data rate with less error protection, to more robust MCS choicesthat provide greater probability of successful transmission at lowerdata rates. The less robust MCS choices use less radio resources for agiven data transmission then are required for the more robust MCSchoices.

Using the prior art method shown in the flow diagram of FIG. 1, once theactivation time expires, the UE is no longer receiving in the sourcecell and data buffered in the source Node B for transmission in thatcell is lost.

The prior art method of recovery of data lost in the source Node B is byradio link control (RLC) layer. The difficulty with the prior art RLCrecovery process is that transmission latency is significantly increasedand the quality of service requirements may not be achieved. If thenumber of PDUs stalled in the source Node B is large, the RLC will needto retransmit a large amount of PDUs, resulting in a longer latency ofPDU transmission. The transmission delay may be increased further by anynew data that is transmitted in the target cell prior to the lost PDUsin the source Node B are known to the sending RLC, since the Node B foreach priority queue schedules transmissions as a FIFO regardless ofwhether the PDUs are initial transmissions or retransmissions. As aresult, upon a serving HS-DSCH cell change when data remains buffered inthe source Node B, PDUs stalled in the source Node B can result insignificant transmission latency for those PDUs.

It is therefore desirable to reduce and potentially eliminate the amountof data that is stalled in a source Node B upon a serving HS-DSCH cellchange.

SUMMARY

An apparatus and method in accordance with the present invention reducethe amount of data that is stalled in a source Node B after a servingHS-DSCH cell change in a communication system that includes an RNC andat least one Node B. In a first embodiment the RNC temporarily suspendsdata transmissions from the RNC to the Node B. In a second embodiment,the activation time is used in data scheduling. In a third embodiment, amore robust MCS level is selected to apply to the data. In a fourthembodiment flow control is employed for the data transmitted between theRNC and the Node B.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram of the actions taken by a prior art Node B andRNC as part of a serving HS DSCH cell change.

FIG. 2 is a flow diagram of the actions taken by a Node B and an RNC inaccordance with a first embodiment including employing the suspension ofdata as part of a serving HS-DSCH cell change.

FIG. 3 is a flow diagram of the actions taken by a Node B and an RNC inaccordance with a second embodiment employing the activation time indata scheduling as part of a serving HS-DSCH cell change.

FIG. 4 is a flow diagram of the actions taken by a Node B and an RNC inaccordance with a third embodiment employing the activation time in MCSselection as part of a serving HS-DSCH cell change.

FIG. 5 is a flow diagram of the actions taken by a Node B and an RNC inaccordance with a fourth embodiment employing flow control as part of aserving HS-DSCH cell change.

FIG. 6 is a flow diagram of the actions taken by a Node B and an RNC inaccordance with a fifth embodiment employing all of the techniques shownin FIGS. 2-5 as part of a serving HS-DSCH cell change.

DETAILED DESCRIPTION

The present invention will be described with reference to the drawingfigures wherein like numerals represent like elements throughout.

Referring to the flow diagram of FIG. 2, the first embodiment for themethod 10 of the present invention is shown. This embodiment temporarilysuspends data transmissions from the serving RNC (hereinafter RNC) tothe Node B. Once the RNC recognizes the need for a serving HS-DSCH cellchange (step 12), the RNC suspends all data transmissions to the sourceNode B (step 14). As those of skill in the art will appreciate, thereare many different mechanisms the RNC may use to suspend datatransmissions. For example, the RNC may suspend transmissions by forcingthe RLC entity enter into the “Null State”, or by applying suspend andresume techniques during which the RLC does not transfer any PDUs. Itshould be noted that the specific method used to suspend datatransmissions from the RNC is not important; only the fact that they aresuspended. In any event, regardless of the method used to suspend datatransmissions, suspending data transmissions to the source Node B willensure that new data will not continue to be forwarded to the sourceNode B for buffering and thus, possible stalling.

The RNC then sends a reconfiguration message to the Node B (step 16).The reconfiguration message notifies the Node B of the serving HS-DSCHcell change. This initiates a series of events such that the UE willstop listening to the HS-DSCH in the source cell and start listening theHS-DSCH in the target cell.

The scheduler (not shown) in the Node B schedules data to the UEs (step18) in accordance with prior art methods, which are typically based uponthe priority class of the data and/or the latency requirements of thedata. Once the data is scheduled at step 18, the Node B applies theappropriate MCS level based upon UE feedback (step 20) and transmits thedata to the UEs. The Node B attempts to successfully transmit all thePDUs in the priority buffers (in the MAC-hs) belonging to the UE. Theactivation time then expires (step 22) if the activation time isincluded in the reconfiguration message. However, if the activation timeis not included in the reconfiguration message or utilized in thisembodiment, then in step 22, the UE stops listening to the source NodeB.

In accordance with this first embodiment of the present invention, sincethe data transmissions have been suspended at step 14, it is more likelythat the source Node B will be able to transmit all buffered data to theUE before the UE stops listening to the source Node B. Data left in thesource Node B after the serving HS-DSCH cell change is useless and willnot be transmitted to the UE. It is the responsibility of the higherlayer, the RLC, to recover the lost data. The recovery procedure of thehigher layer creates larger data transmission latency.

Referring to the flow diagram of FIG. 3, a second embodiment for amethod 30 in accordance with the present invention is shown. Thisembodiment utilizes an activation time as a new criteria to scheduledata to a UE that is undergoing an HS-DSCH cell change. Once the RNCrecognizes the need for a serving HS-DSCH cell change (step 32), the RNCthen sends a reconfiguration message to the Node B (step 33). Inaccordance with this embodiment, the reconfiguration message includes anactivation time, which is an explicit moment in time known in the Node Bwhen the UE will stop listening to the HS-DSCH in the source cell andstart listening the HS-DSCH in the target cell. In current 3G systems,the activation time, if present, is included in the message “Radio LinkReconfiguration Commit” of the NBAP message.

The Node B schedules data (step 34) to the UEs based, at least in part,upon the activation time by providing more resource allocations thenwould normally be given to the user in the time interval ending at theactivation time of the HS-DSCH cell change. The Node B scheduler mayachieve this by, for example, giving a higher priority to datatransmissions of the UE and/or by adjusting the latency requirements ofthe data for that UE to provide a greater resource allocation than wouldnormally be given to the UE in the time interval ending at theactivation time of the HS-DSCH cell change. The appropriate MCS level isselected based upon UE feedback (step 35). If there are not enough radioresources for the source Node B to transmit all the PDUs by theactivation time, the source Node B attempts to transmit the PDUs as manyas possible taking into account requirements of other UEs within thecell. The activation time then expires (step 36).

Although the activation time provides a “time certain” by which the NodeB should complete the transmission of data to the UE undergoing theserving HS-DSCH cell change, the activation time is not necessary toemploy the teachings of this embodiment. Accordingly, as an alternativeto the second embodiment, the activation time is not sent as part of thereconfiguration message and is not utilized to schedule the data. Inthis alternative, once the Node B receives the reconfiguration message,it begins to schedule the data (step 34) to the UEs such that moreresources are allocated to the UE undergoing the serving HS-DSCH cellchange. The MCS level is then selected (step 35). Since the activationtime is not included in the reconfiguration message or utilized in thisalternative to the second embodiment, in step 22 the UE stops listeningto the source Node B.

In accordance with this second embodiment of the present invention,since the data has been scheduled at step 34 giving more resources tothe UE undergoing the serving HS-DSCH cell change, (whether or not theactivation time is utilized), the UE undergoing the serving HS-DSCH cellchange will successfully receive more of the source Node-B buffered datathan if the cell transmission scheduling algorithm did not give moreresources to that UE undergoing the serving HS-DSCH cell change.

Referring to the flow diagram of FIG. 4, a third embodiment for a method40 in accordance with the present invention is shown. This embodimentapplies a more robust MCS level to the data destined for the UEundergoing the serving HS-DSCH cell change than the appropriate MCSlevel based solely on UE feedback. Once the RNC recognizes the need fora serving HS-DSCH cell change (step 42) the RNC sends a reconfigurationmessage to the Node B (step 46) which includes the activation time. TheNode B schedules data to the UEs based upon the priority and latency ofthe data (step 48), as is similar to current scheduling methods. TheNode B then applies a more robust MCS level than the appropriate MCSlevel based on UE feedback (step 50) in consideration of the activationtime. The activation time then expires (step 52). Applying a more robustMCS level implies the use of more radio resources. By choosing a morerobust MCS the probability of successful delivery of data to the UE isincreased.

As aforementioned, although the activation time provides a “timecertain” by which the Node B should complete the transmission of data tothe UE undergoing the serving HS-DSCH cell change, the activation timeis not necessary to employ the teachings of this third embodiment.Accordingly, as an alternative to the third embodiment, the activationtime is not sent as part of the reconfiguration message and is notutilized to select the MCS level to transmit the data. In thisalternative, once the Node B receives the reconfiguration message and itbegins to schedule the data to the UEs (step 48), it selects a morerobust MCS level at step 50 such that more resources are allocated tothe UE undergoing the serving HS-DSCH cell change. The activation timeis not necessary. Since the activation time is not utilized, at step 52the UE stops listening to the source Node B.

In accordance with this embodiment of the present invention, since theMCS levels are selected to allocate more resources to the UE undergoingthe serving HS-DSCH cell change, (whether or not the activation time isutilized), the UE undergoing the serving HS-DSCH cell change will mostlikely receive more of its data in the source cell then if the selectionof the MCS levels did not allocate more resources to the UE undergoingthe serving HS-DSCH cell change.

Referring to the flow diagram of FIG. 5, a fourth embodiment for amethod 80 in accordance with the present invention is shown. Thisembodiment eases flow control on the data flow between the RNC and theNode B such that all of the data destined for the UE undergoing theHS-DSCH cell change is sent as quickly as possible to the Node B. Oncethe RNC recognizes the need for a serving HS-DSCH cell change (step 82)the RNC sends a reconfiguration message to the Node B (step 86). Thereconfiguration may or may not include the activation time.

The Node B then eases flow control (step 88) on the data flow betweenthe RNC and the source Node B that is destined to the UE undergoing theHS-DSCH cell change. Essentially, flow control speeds up transmission ofthe data that is in the pipeline between the RNC and the source Node B.The intention is to maximize successfully transmitted data before the UEstops listening to the source Node B. Therefore it is necessary toforward data maintained between the RNC and Node B as soon as possibleso that the scheduler in the source cell has greater ability process alldata for the UE undergoing the HS-DSCH cell change before the UE stopslistening to the source Node B.

The Node B then schedules data to the UEs based upon the priority andlatency of the data (step 90). Once the data is scheduled at step 90,the Node B applies the appropriate MCS level (step 92) based upon UEfeedback, which is consistent with prior art MCS selection methods.

The data is then transmitted to the UEs. The Node B attempts to transmitall the PDUs belonging to the UE as soon as possible, or before theactivation time is expired if an activation time is present in thereconfiguration message from the RNC to the Node B. If there are notenough radio resources for the source Node B to transmit all the PDUs intime, the source Node B attempts to transmit as many PDUs as possible.The activation time then expires (step 94). If the activation time isnot utilized in this embodiment, then in step 94 the UE stops listeningto the source Node B.

In accordance with this embodiment of the present invention,implementing flow control at step 88 increases the chances that all ofthe data will be more timely received by the Node B.

It should be understood by those of skill in the art that any of thetechniques employed in the four embodiments shown in FIGS. 2-5 may beused separately or together in various combinations. Referring to theflow diagram of FIG. 6, an example embodiment for a method 100 inaccordance with the present invention is shown. This embodiment: 1)utilizes the activation time as one of the criteria in scheduling of thedata to the UE; 2) applies a more robust MCS level to the data; andeither 3) suspends data transmissions from the RNC to the Node B afterrecognizing the need for a serving HS-DSCH cell change; or 4) employsflow control to the data that is in the pipeline between the RNC and theNode B. It should be noted that suspending data transmissions andperforming flow control are mutually exclusive. If data transmissionsare suspended, flow control cannot be pursued. Likewise, if flow controlis desired, suspension of data transmissions cannot be performed.Accordingly, these steps will be referred to as optional in reference toFIG. 6, although it should be understood that both steps cannot beperformed together.

Once the RNC recognizes the need for a serving HS-DSCH cell change (step102) the RNC may optionally suspend all new data transmissions to theNode B (step 104). The RNC then sends a reconfiguration message to theNode B (step 106). The reconfiguration message may include theactivation time. Steps 104 and 106 may be performed in any order, butsuspending data transmissions (step 104) is preferably first, since databuffered in the source B Node is minimized.

Optionally, flow control is then exhibited on the data buffered at theRNC such that all of the data buffered at the RNC is sent to the Node Bas quickly as possible (step 108).

The Node B schedules data to the UEs based upon the activation time,priority and latency of the data (step 110). As aforementioned withrespect to the embodiment shown in FIG. 3, using the activation time asone of the scheduling criteria increases the amount of radio resourcesdirected to the particular UE in order to increase the amount ofsuccessfully transmitted data in advance of the activation time.However, if the activation time is not sent as part of thereconfiguration message and is not utilized to schedule the data, oncethe Node B receives the reconfiguration message, it begins to schedulethe data to the UEs such that more resources are allocated to the UEundergoing the serving HS-DSCH cell change in order to get data to thatUE as quickly as possible.

Once the data is scheduled at step 110, the Node B applies a more robustMCS level (step 112), based upon not only UE feedback, but also theactivation time. As aforementioned with respect to the embodiment shownin FIG. 4, using the activation time as one of the criteria to adjustthe MCS level increases the possibility of successful delivery andavoids the need for retransmissions. However, if the activation time isnot sent as part of the reconfiguration message and is not utilized toapply the MCS level, once the Node B receives the reconfigurationmessage, it applies a more robust MCS level to the data destined to theUE undergoing the HS-DSCH cell change such that more resources areallocated to that UE data is sent to that UE as quickly as possible.

The data is then transmitted to the UEs. The Node B attempts to transmitall the PDUs destined to the UE undergoing the HS-DSCH cell changebefore the activation time is expired, or as quickly as possible. Ifthere are not enough radio resources for the source Node B to transmitall the PDUs in time, the Node B attempts to transmit the PDUs as manyas possible. The activation time then expires (step 114). If theactivation time is not utilized in this embodiment, then in step 114 theUE stops listening to the source Node B.

1. A Node B configured to receive and buffer comprising: a receiverconfigured to receive a notification of a high-speed downlink sharedchannel (HS-DSCH) cell change for a user equipment (UE); a schedulerconfigured to schedule data for transmission to the UE to producescheduled data by allocating resources, wherein a greater amount ofresources are allocated to data for transmission to the UE than to datafor transmission to other UEs served by the Node B; a modulation andcoding set (MCS) unit configured to apply a modulation and coding setMCS level to the scheduled data using a predetermined MCS level togenerate modulated data; and a transmitter configured to transmit themodulated data to the UE.
 2. The Node B of claim 1 wherein thenotification includes an activation time, which indicates when the UEwill cease communicating within the cell.
 3. The method of claim 2wherein the transmitter is configured to transmit the modulated data tothe UE prior to the activation time.
 4. The Node B of claim 1 whereinthe Node B is further configured to perform flow control, such that datafor transmission to the UE is sent at a higher rate from the RNC to theNode B.
 5. A method for efficient delivery of Node B buffered datacomprising: receiving at a Node B a notification of a high-speeddownlink shared channel (HS-DSCH) cell change for a user equipment (UE)communicating with the Node B within a cell; scheduling data at the NodeB for transmission to the UE to produce scheduled data by allocatingresources, wherein a greater amount of resources are allocated to datafor transmission to the UE than to data for transmission to any other UEserved by the Node B; applying a modulation and coding set (MCS) levelto the scheduled data using a predetermined MCS level to generatemodulated data; and transmitting the modulated data to the UE.
 6. Themethod of claim 5 wherein the receiving a notification is such that thenotification includes an activation time, which indicates when the UEwill cease communicating within the cell.
 7. The method of claim 6wherein the scheduling data at the Node B is such that the data fortransmission to the UE is sent to the UE prior to the activation time.8. The method of claim 5 further comprising performing flow control,such that data for transmission to the UE is sent at a higher rate fromthe RNC to the at least one Node B.
 9. A method for efficient deliveryof buffered data comprising: determining at a radio network controllerRNC a need for a high-speed downlink shared channel HS DSCH cell changefor a user equipment UE communicating with a Node B within a cell;generating a notification at the RNC to the Node B regarding the cellchange; suspending at the RNC all further data transmissions to the NodeB for the UE; and sending from the RNC to the Node B the notification.10. A method for efficient delivery of data comprising: determining at aradio network controller RNC a need for a high-speed downlink sharedchannel HS-DSCH cell change for a user equipment UE communicating with aNode B within a cell; generating a notification at the RNC to the Node Bregarding the cell change; sending from the RNC to the Node B thenotification; and performing flow control at the RNC, such that data fortransmission to the UE is sent at a higher rate from the RNC to the NodeB.